The present invention relates to a method for assembling frames of a multiframe by calculating, for each of the frames, the value of an identifier for inclusion into each of the frames before transmitting them at the rate of a transmitter clock, wherein the frames are temporarily stored in a temporary buffer of a receiver before reading them out from the temporary buffer for storage to a multiframe buffer memory of a receiver, and to a frame receiver device comprising a temporary buffer adapted to temporarily store incoming frames, a multiframe buffer memory coupled to the temporary buffer and adapted to store incoming frames received from the temporary buffer.
It is well known that in many ATM-TDM systems, such as for instance the APON system, which is the abbreviation of asynchronous passive optical networks, ATM cells transmitted at a transmitter, for instance an optical line termination unit, hereafter abbreviated as OLT, have to be recombined in the correct sequence at the receiver. This is especially true in case Channel Associated Signalling, is used. In this case, a multiframe is composed of 16 previously sent TDM frames, to be completed with specific Channel Associated Signalling information for further use by a downstream user. In case these frames can arrive asynchronously, and not in the sequence they were previously sent by the transmitter, for instance due to cell delay variation problems, the only solution for properly assembling them in the multiframe was to first temporarily buffer them in a temporary buffer memory, after which, if all 16 frames were received, they could be read out from this memory for assembly into the multiframe buffer memory. Such a straightforward method thereby not only requires a large temporary buffer memory, but also introduces an additional delay because of this temporary storage action. Furthermore this solution implies that within each transmitted frame, an identifier having a number of 1 to 16 is to be included, so as to allow the correct positioning of the TDM frame into the multiframe memory. In the previously mentioned APON system, however, the TDM frame is limited in the sense that only 3 bits can be included for this identifier as is standardized by the ITU-T specification 363.1. This makes it nearly impossible to use this prior art solution, since with 3 bits, only 8 different memory addresses can be accessed.
The additional delay is thereby also not acceptable for envisaged applications such as leased line services where delay requirements of 625 to 650 microseconds are common.